AuroraRuntime/Source/Threading/Primitives/AuConditionEx.cpp

/***
    Copyright (C) 2021 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: AuConditionEx.cpp
    Date: 2021-6-12
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "AuConditionEx.hpp"
#include "AuMutex.Generic.hpp"
#include "AuSemaphore.Generic.hpp"

namespace Aurora::Threading::Primitives
{
    // Implementing Condition Variables with Semaphores, Andrew Birrell, MSFT
    // Subsitute semaphore count = 1 with a spinlock and...
    struct SemaphoreConditionVariableImpl : ConditionEx
    {
        SemaphoreConditionVariableImpl();

        void WaitForSignal(Aurora::Threading::IWaitable *pWaitable) override;
        void WaitForSignal(const AuSPtr<Threading::IWaitable> &pWaitable) override;
        void WaitForSignal() override;
        void Signal() override;
        void Broadcast() override;

    private:
        std::atomic<AuUInt> waiters_;
        Semaphore s_, h_;
        SpinLock x_;
    };

    SemaphoreConditionVariableImpl::SemaphoreConditionVariableImpl() :
        s_(0),
        h_(0)
    {

    }

    void SemaphoreConditionVariableImpl::WaitForSignal(Aurora::Threading::IWaitable *pWaitable)
    {
        return WaitForSignal(AuUnsafeRaiiToShared(pWaitable));
    }

    void SemaphoreConditionVariableImpl::WaitForSignal(const AuSPtr<Threading::IWaitable> &pWaitable)
    {
        this->x_.Lock();
        this->waiters_++;
        this->x_.Unlock();

        if (pWaitable)
        {
            pWaitable->Unlock();
        }
        
        this->s_.Lock();
        this->h_.Unlock();

        if (pWaitable)
        {
            pWaitable->Lock();
        }
    }

    void SemaphoreConditionVariableImpl::WaitForSignal() 
    {
        WaitForSignal(nullptr);
    }

    void SemaphoreConditionVariableImpl::Signal() 
    {
        this->x_.Lock();
        if (this->waiters_ > 0)
        {
            this->waiters_--;
            this->s_.Unlock(); // 1 may pass
            this->h_.Lock();   // finish operation - wait for the alive signal back
        }
        this->x_.Unlock();
    }

    void SemaphoreConditionVariableImpl::Broadcast()
    {
        this->x_.Lock();
        this->s_.Unlock(this->waiters_); // all may pass at once
        for (auto i = 0; i < this->waiters_; i++)
        {
            this->h_.Lock();      // finish operation - wait for the alive signal back
        }
        this->waiters_ = 0;
        this->x_.Unlock();
    }

    AUKN_SYM ConditionEx *FeaturefulConditionNew()
    {
        return _new SemaphoreConditionVariableImpl();
    }

    AUKN_SYM void FeaturefulConditionRelease(ConditionEx *pCVEx)
    {
        AuSafeDelete<SemaphoreConditionVariableImpl *>(pCVEx);
    }
}